Browsing by Author "Masambi, Saviour"
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- ItemEvaluation of precipitation processes for the removal of iron from chloride-based copper and nickel leach solutions(Stellenbosch : Stellenbosch University, 2015-12) Masambi, Saviour; Dorfling, Christie; Bradshaw, S. M.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: A process route is being developed to recover nickel and copper from chloride leach solutions contaminated with iron. The concentrations of nickel and copper are approximately 3 g/L each, while that of iron is about 45 g/L. Iron contamination causes problems in processes typically used for the recovery of nickel and copper from leach solutions, such as solvent extraction or sulphide precipitation. This study focused on the removal of iron from the chloride-based leach solution. Iron is commonly removed from hydrometallurgical solutions by the process of precipitation. In the leach solution under investigation, iron mainly exists as iron(II) chloride. Iron(II) generally precipitates at pH above 7 while iron(III) can be precipitated at pH above 0. In this study, it was desired to oxidize iron(II) to iron(III) using oxygen gas at a temperature below 100oC and to subsequently precipitate iron(III). It was sought to produce an environmentally friendly precipitate, with minimal nickel and copper co-precipitation and easily separate the solids from the liquid. The effect of hydrochloric acid and copper concentration on the rate of iron(II) oxidation were experimentally determined. Several concentrations of hydrochloric acid, ranging from about 0.7 M to 6.4 M, were investigated while the copper concentrations investigated were 0.3 g/L and 3 g/L. The effects of temperature (40oC, 60oC, 80oC and 90oC), pH (0, 1, 2 and 3) and 30 g/L seeding on the quality and extent of iron removal were experimentally determined. The conventional hematite precipitation process was compared to the iron phosphate process in terms of iron removal, nickel and copper co-precipitation, and solid-liquid separation. The experiments were conducted in a 1.6 L glass reactor using synthetic as well as plant solutions. Synthetic solutions contained about 45 g/L iron, 3 g/L nickel and copper. Plant solutions contained significantly higher iron and nickel, with traces of copper. The concentrations of iron and nickel in plant solutions were approximately 120 g/L and 12 g/L respectively. The rate and extent of oxidation of iron(II) , using synthetic solutions, increased with both acid and copper concentrations. Experimental data and equilibrium calculations were used to prove that the mole ratio of associated acid to iron needed to be greater than or equal to 1 for rapid oxidation of iron(II) to occur. It was experimentally shown that oxidation in the presence of 3 g/L copper concentration yielded higher iron(III) compared to oxidation in the presence of 0.3 g/L copper concentration under uniform conditions. Iron precipitation from synthetic solutions was complete at all pH points investigated (0, 1, 2, 3) in both iron phosphate and hematite precipitation processes. The co-precipitation of nickel and copper increased with pH for both precipitation processes. The co-precipitation of nickel and copper in the iron phosphate process increased with an increase in temperature from 40oC while the co-precipitation of nickel and copper increased with reduction in temperature from 80oC in the hematite precipitation process. Seeded iron phosphate precipitation at pH 1 and 40oC resulted in over 99% iron removal with averages of 5% and 11% nickel and copper co-precipitation respectively. Increasing the pH to 3 resulted in complete iron removal at the expense of over 50% losses in nickel and copper. Seeded hematite precipitation at pH 1 and 80oC yielded over 99% iron removal with averages of 6.5% nickel and 7% copper losses. Upon increasing the pH to 3, nickel and copper losses were above 35%. The iron phosphate precipitation was complete within 30 – 60 minutes while hematite precipitation was complete after 60 – 120 minutes. All seeded precipitation experiments produced easily filterable precipitates. Attempts to precipitate unseeded hematite at 80oC and pH 1 resulted in higher nickel and copper losses (about 16% and 27% respectively), with the precipitates practically impossible to filter. The unseeded iron phosphate precipitates produced at 40oC and pH 1 were filterable however relatively higher losses of nickel and copper were observed (about 11% and 22% respectively). Settling experiments showed that iron phosphate precipitates completely settled within 26 minutes. Hematite precipitates did not settle after 8 h. Plant solutions were tested to validate the direct applicability of the results obtained using synthetic solutions. It was observed that complete oxidation was achieved after 180 minutes. Iron phosphate precipitation at pH 1 and 40oC achieved complete iron removal after 60 minutes and nickel losses of approximately 7.8% after 120 minutes. Hematite precipitation at pH 1 and 80oC resulted in complete iron removal after 60 min and nickel co-precipitation of 12% after 120 minutes.